Sectional boiler



May 3, 1960v J. G. MUELLER 2,935,052

SECTIONAI.. BOILER F'iled Dec. 27, 1956 4 Sheets-Sheet 1 INVENIOR.

May 3, 1960 J. G. MUELLER 2,935,052

SECTIONAL BOILER Filed Dec. 27, 1956 4 Sheets-.Sheet 2 INVENTQR.

May 3, 1960 J. G. MUELLER 2,935,052 SECTIONA; BOLER F'i'led Dec. 2'7, 1956 4 Sheets-Sheet 3 INVENTOR.

a@ lq Si JJM@ new May 3, 1960 Filed Dec. 27, 1956 J- G. MUELLER SECTIONAL BOILER 4 Sheets-Sheet 4 INVENTOR. Wm

SECTIONAL BOILER Johannes G. Mueller, Michigan City, Ind., assgnor to Weil-McLain Company, Michigan City, Ind., a corpo? ration of Delaware Application December 27, 1956, Serial No. 630,899

'6 Claims. (Cl. 122-225) This invention relates to heating equipment, and more particularly to a boiler for hot water and steam.

In general this invention is concerned with improve- Yments in the internal construction for boilers for obtainving increased efiiciency in operation, and is applicable to smaller, for example domestic-size boilers, as well as to larger boilers as are used in heating plants for larger buildings. For purposes of describing a preferred form 4of the invention, however, it is shown embodied in a domestic size sectional type boiler, that is, a boiler unit made up of a plurality of individual inverted U-shaped sections which are fastened together by'mechanical connecting devices and mounted on a base which accommol'dates a refractory combustion chamber. Two primary features of internal construction of boilers govern boiler operation. These are (l) the ratio of direct and indirect heating surface, and (2) the character of `llue gas travel through the boiler which is produced by the bale and passage `arrangement employed. The primary heating surfaces rare those surfaces in the boiler exposed to theflame of combustion, while the secondary surfaces are all the remaining surfaces over which the hot ilue gases travel.

It is a general object of the invention to provide an improved internal construction for boilers which obtains a more economical ratio of direct and indirect heating surface and a more efficient type of ilue gas travel.

A primary advantage offered by sectional type boilers is that the same individual sections may be used in the erection of boilers of different sizes. It is a major object of the present invention to provide a sectional boiler offering better performance, lower draft loss, and higher over-all efficiency over a given series of different sizes, by reason of a new concept in boiler construction, namely, self-regulating flue `gas travel. By controlling ue gas travel, even combustion is produced throughout the length of the boiler irrespective of the number of sections yand the performance vcharacteristics remain substantially the same for all boilers of a series.

It is an object of the invention to provide means for insuring that all boiler sections of a sectional boiler contribute equally in the transfer of heat to the heating surfaces by controlling iloW of ilue gases in a pattern such as provides optimum heat transfer. Another object is to provide a boiler where the boiler internally is uninterrupted by flue gas baies, and where the natural draft is employed to force the flue-gases to the heating surfaces at the sides of the boiler, and then to la central horizontal llue gallery which leads the ilue gases to the chimney, land thus into wiping contact with a greater area of water-backed heating surface.

Another object of the invention is to provide a new and improved sectional boiler, the construction of which facilitates erection, operation and maintenance. A related object is to provide a sectional boiler construction which may be more readily dismantled. More specifically, it is an object to provide an improved means for sealing between adjacent boiler sections and one which (accomplished.

2,935,052 `Patented May 3, 1960.

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remains intact when the boiler sections are separated so as to be available to reseal the boiler when the sections are rejoined together, after repair or cleaning has been It is another'related vobject to provide sealing means employing an asbestos rope between boiler Ysections and where the rope is received in such a manner as to -cause it to more effectively seal the boiler whenl plates. VIt is a further and a related object to provide means for securely locking the cleanout plates in position in the boiler.

Other objects will appear from the following description taken in connection with the accompanying drawings, wherein:

Figure l is a perspective view of a partially erected Ysectional-type boiler embodying this invention, with parts broken away to illustrate the internal constructional details of the boiler;

Fig. 2 is a sectional view, taken in the offset planes of lines 2-2 of Figure l, and illustrates the internal `construction of the boiler of Figure l, with the center part of the boiler broken away and the front and back sec- .tions in place;

Figs. 3, 4 and 5 are front elevation views of the front, intermediate and back sections, respectively, of the boiler illustrated in Figs. 1 and 2;

Fig. 6 is a sectional view of the boiler of Figs. l and 2 taken in the plane of line 6--6 of Fig. 2;

Fig. 7 is a sectionalrview of this boiler taken in the plane of line 7--7 of Fig. 2;

Fig. 8 is an enlarged sectional view taken in the plane of lines 8 8 of Fig. 7, and illustrates the sealing means employed for sealing between adjacent sections of the boiler; l

Fig. 9 is a fragmentary section taken inthe plane of lines 9-9 of Fig. 2, and illustrating a mounted cleanout plate; and

Fig. 10 is a fragmentary section taken in the plane of lines 10-10 of Fig.A 9, and again illustrating the construction of the cleanout plate and locking means therefor.

While the invention is susceptible of various modications and alternative constructions, there is shown'n the drawings and will be herein described in detail a preferred embodiment of the invention. It is to be understood, however, that it is not thereby intended to limit the invention to the specific form disclosed, but, on the contrary, it is intended to cover all modifications, al'- ternative constructions and equivalents falling Within the spirit and scope of the invention as expressed in the appended claims.

Turning now to the drawings, Figure l illustrates a sectional-type boiler, with the front section removed, designated with the general reference numeral 10, in which the present invention is incorporated. It is recognized tnat sectional boilers have been known heretofore, and in general boilers .of this type ern-body U-shaped sections 11 erected on a base accommodating a refractory iirebox 12, andA provided as illustrated in Figure 1, to mount a burner in place on the front of the boiler. Hot ue gases are produced by ame in the firebox, and pass throughthe boiler to a smoke collar 14 (Fig. 2) which serves to lead the gases to the chimney. The smoke collar is fastened on the back section and receives ue gases froma collector constructed as horizontal flue galleries 15, @the collector being in communication with the smokecollar through thesmoke opening in the outer wall of the back section casting;

As stated hereinbefore, the present invention introduces the new concept of self-regulating flue gas travel. By controlling the travel of hot flue gases through the boiler, optimum heat transfer to the primary and secondary heating surfaces may be obtained, and as well, the jhot gases may be forced into wiping contact with av greater area of water-backed sur-face. Water for the generation of steam, or to be heated for supply to a hot water system, circulates through an internal header 16 (Figure 1.) and through water passages `17 formed by coring the castings for each boiler section. As will be observed from a careful examination `of Figure 1, the individual sections of the boiler are cast so as to form the water passages 17 within each individual section. The internal header 16 is `formed by connecting the upper nipple openings 18 by slip nipples 19, and a pipe 20 connected to the header eX- tends to the heating system. The boiler sections also are so` constructed as to provide passages 21 for flue gas between each boiler section. For this purpose each side lof the individual boiler sections is formed so that when the sections are connected together vertical uptake passages 21 are left between each section at vboth sides of the boiler, leading to the horizontal tlue galleries centrally of the boiler which communicates with the smoke collar and the chimney.

For transferring heat to the water circulating through the header 16 and the water passages 17 in the sections of the boiler, the flue 4gases in the iirebox` by natural draft created from the chimney, are forced laterally towards the outer wall of the boiler to pass upwardly 'cetween the individual boiler sections through thevertical uptake passages Z1. Being formed between i adjacent boiler sections, these uptake passages, as will beV seen in yFigure l, open in their lower part to the arched region of the finned iirebox crown 22. The vertical limits of the uptake passages 21 are defined by the rounded upper corners of the boiler itself, which form turn-around passages 21' and these passages 21 are disposed laterally of the horizontal ilue gas galleries 15 with which the uptakes 21 communicate and into which the hot ue gases pass via the turn-around passages after flowing through the vertical uptakes. ySince at each side and between every section of the boiler, `a vertical uptake is formed, the hot ilue gases in the rebox are divided into a plurality,

fthe number being determined by the number of sections,

of individual streams of gases, and these streams of gases iiow into the horizontal flue galleries 15. For a purpose to be later described, certain of the uptakes 21 are of somewhat larger cross-sectional area than the others. The difference in area which is present, however, does not result in a substantial difference in resistance to llow of ue gas as between the different size uptakes. Therefore, e'ach of the uptakes of the boiler receives a substantially equal share of the total volume of the flue gas produced in the combustion chamber. A

To force the ilue gases into a greater number of'waterbacked passages, the collector through which' the gases pass in their travel to the chimney, in the present instance is divided into four spaced and parallel ue galleries 15 by centrally arranged hollow, vertical and horizontal webs 25, 26 forming additional water passages 27 to promote the circulation of Water and to provide additional heating surface 28. In order to force the gases as they travel towards the back of the boiler into the lower pair 29, 30 of flue gallery passages, as seen in Figure l, the cross-sectional area of these passages is made somewhat Vlarger in size than the cross-sectional area of the upper flectorinto parallel passages or galleries 15 and forcing Athe flue gases into the lower passages, contributes towards obtaining balanced horizontal flue travel equalizing the heat absorption of secondary heating'surfaces.

As a further means for obtaining balanced flue travel and equalized heat absorption throughout the entire length of the boiler, selectively certain of the vertical uptake passages of the boiler are enlarged in cross-section. In the present arrangement, and as exemplary only, the vertical uptakes 39 formed between the front end section 40 (Fig. 2) and the adjacent intermediate section 41 are made larger than the uptakes 21 between the other sections of the boiler. The'etfect of the larger crosssection for the uptake pair 39 at the sides of the boiler in the region of the tiring, is to force -a greater portion of the `flue gases produced in the rebox through these larger yarea uptakes. Natural draft drawing ilue gases from the iirebox to the chimney, would ordinarily tend to short circuit those flue gas passages at the front end of the boiler, and by enlarging the uptake area and reducingthe fric- Vtion loss, the draft through the boiler has the effect of yforcing the flue gases through those uptakes into regions of the boiler which without' such a provision would receive a lower volume of flue gases. A 'further' feature contributing to balanced flue gas travel -is obtained as a result of forming the'uptakes 21 regular in cross-section, as shown in Fig. 2, and employing the turn-around passages 21, which introduce greater resistance to iiue gas flow than is offered by the uninterrupted uptake passages. Moreover, by tapering the uptakes 21, as shown in Figs. V3 5, -from a larger cross-sectional area at 21" where the uptakes 21 open into the combustion chamber, the velocity of the flue gas remains uniform the length of the uptakes, notwithstanding the temperature drop of the gas occurring as it passes through the uptake, thus obtaining uniform heat transfer.

Enlarging the uptake area adjacent the front end section of the boiler shown as exemplary in the drawings of this application, adds an additional important effect, namely obtaining substantially uniform boiler performance for all boiler sizes of a series. This aspect of the invention may best be explained by reference to an actual example of boiler construction, a boiler designed for a larger type residence and for ring by an oil burner. As has been set forth above, different size boilers made of the same boiler sections may be erected by using a dilerent number of like intermediate sections with the same front section and back section. In theory, by means of the present invention, boiler performance would be substantially uniform irrespective of the number of sections employed in the boiler. For example, from a four section boiler to the largest of a series including an infinite number of sections. As a practical matter, however, there is a limit to boiler length, and from that standpoint and from others such as ease in erection, it is preferred and contemplated that several series of boiler sizes will be provided. Of course, in each series only are the various front, back and intermediate boiler sectionsrthe same. While there would be some overlap between the largest boiler in the series to the smallest boiler of the next larger series, as the boiler sizes increase the over-all dimensions may become larger so that all the dimensions of the erected unit are kept within reasonable limits. In the present instance, the smallest boiler size withina series would be made of four sections, the largest size, although more sections couldrbe employed, of eight vsections. The middle sizes may be obtained by adding intermediate sections, two only being used for `the smallest, three for the next larger, up to the Ysix intermediate sections required for the largest size boiler. VIn each case the front section and back section would be the same, and in the chosen illustrative' example, the front 40 and back 43 sections of Figs. 3 and 5 respectively, would be employed in the boiler.` The intermediate section 41 shown in Fig; 4, similarly, would be employed'in the illustrative example of the present invention. The smallestI boiler, ofcourse, has the smallest `'capacity and output while 'the largest boiler has the largest output.`

In the present example of a` boiler series, chosen to illustrate this aspect of the invention, measured in terms of actual fuel input (oil), the smallest boiler of the series has'this input:

4-section boiler-2.25 gals. per hour while the largest 4boiler of the series:

8-section boiler-'4.10 gals. per hour.

The -above figures are actual test figures and reect a non-linearity in input, and a corresponding drop over the Vboiler sizes of the series in the input of fuel and likewise in the volume of llue gases produced. Itwill be appreciated that the production of hot ilue gases, the medium for heatingfwaterin the boiler, is in direct proportion Ato the amount of fuel burned. This drop over the whole .seriesmay be computed as follows:

2X2.25 gals. per hr.=4. 50

Actual input =4. 10 l 40 j(Note.'-Twice the input for four sections, if the relation' is llinear', would give the input for eight section unit.) Asdefscribed hereinbefore, the total volume of flue gasesv produced in the firebox is divided by the llarge number zof'vertical uptakes between the boiler sections `ii'ltoa like numberof streams of gases. When dealingv with different boiler sizes, in order to obtain uniform boiler performance, it is necessary that the velocity of the ue gases flowing through the vertical uptakes of the small boiler in the series, for example, the four-section -'boiler above, be maintained substantially the same as the velocity of ue gases flowing through the uptakes of the largest boiler in the series, as` for example the eightsection boiler above. l For obtaining substantially uniform velocity of flue gases for all boilersizesl of a given series, in the -present instance, andas an exemplary form of the invention, the {cross-sectional area of the vertical uptakes 39 between `one-of the end sections 40 and the adjacent intermediate section 41 to it, is made larger than the cross-sectional area of the other vertical uptakes 21. The larger size uptakes 39 should be at the end of the boiler opposite f to the smoke outlet opening, and in the boiler as illus- -ftrated in the drawings of this application, would be in the region of the firing of the boiler. Whether the larger `uptakes are in the front section or in the back section of `the` boiler, therefore, depends upon whether the boiler is --front or back fired, and upon the location of the smoke ,"ou'tlet opening, i.e., whether it is in the back or the front `.of the boiler. Referring to the following further data non `thel example chosen to illustrate this aspect of the inventionz `For equal size uptakes between the sections of a four sectionboiler, in order to obtain the same total crosssectional' area, each uptake would be required to be 7 uq. in. in size.

section boiler ltotal with equal (7") size uptakes=98 .sqtin' f Y With selectivelyTV diierent size uptakes the actual tota1 lmi uptake area= sq. in. Percentagewise this difference:

i 98-90=8 sq.ii1.

.input overthe series Aof from four to eight sections of the boiler of the chosen example, is 8.8%. The 8% less cross-sectional area of the uptakes of the eight section boiler substantially matches the non-linearity in input. Consequently the yvelocity of flue gases in the largest boiler size is maintained `substantially the same as the velocity of ue gases in the smallest boiler size in the series. As will be clear to a man skilled in the art, the same holds true for the intermediate sizes and thus boiler performance is made uniform from this standpoint over the entire series.

vIn general mathematical terms, the relation between the total uptake area and the area of the individual uptakes may belexpressed as follows:

Y It will be readily appreciated there are other factors contributing to boiler performance which may be nonlinear `as the boiler sizes vary, however, by compensating for the major non-linear factor, substantially uniform performance may be obtained from the same section (front, intermediate, and back) sold to be erected into different boiler sizes.

In the erection of the boiler shown as exemplary in the drawings, taking for illustration the four section unit of Fig. I2, the front section 40 is rst placed on top of a rectangular, usually cast-iron, base y45 and a slip nipple 19- is installed in the upper slip nipple opening 18 to form the internal header 16. Before adding another section, it is also necessary to clean the smaller, lower nipple openings 46 for receipt of the lower nipples 47 which are pounded in place to form part of the water passage system of the boiler. As will be seen from Fig. 3, which illustrates the frontsection 40 of the boiler in elevation, this section is cast with lands 50 around rwall S4 of the erected boiler and also define the collector Apassages (15) internally of the boiler.

For sealing between Vmeeting lands on adjacent sections of the boiler, and thus for sealing between every section of the boiler, the lands are grooved or channeled for receiving sealing material. In the present instance heat resistant flexible rope such as asbestos rope 55 is used for the sealing material. In the erection of the boiler this rope is draped around the outer wall 54 of the boiler and laid in the grooves or channels 56 found in the lands 50 there. Similarly, centrally of the section about the collector, asbestos rope is laid in the groove 57 of the land 51 forming a U. It is preferred that the asbestos rope should be spot-glued 58 in place in the (Fig. 8) curved sealing grooves, using adhesive. As will be readily appreciated, this also facilitates erection of the boiler because the asbestos rope is held in place. So that the sealing material may remain intact upon dismantling of the boiler, the adhesive should be applied v outside edges 64, 65 of the outer wall.

is made denser and gas'impervious.V

v able plate 73 for closing the same.

7 only to one side of the asbestos rope in the grooved lands of one section of the boiler. Afterv the asbestos rope has been placed on the front section, the upper and lower nipple openings of an intermediate section`41 are Ithen prepared for receiving the nipple, and this section (Fig. 4) is placed on the base 45. 'Ihis intermediate section 41 is then driven against the front section I40 with a heavy Yr'nallet o'r the like to start the'nipples into the lower openings and into the upper ports or openings of that section. At this point, the draw rods 59 are assembledV on the sides of the boilers and the intermediate section is then connected by means of these draw -rods to the front section 40.

The remaining sections are then assembled in place following the same sequence of steps. In a four section boiler, for example, another intermediate section is erected and then a back section 43 klike that shown in Fig.r 5 is installed in the same manner as `the front section 4G and the rst intermediate section 41.

. For insuring a perfect seal between boiler sections, the

grooved or channeled lands 50, 52y forming the outer wall 54 of the boiler are fashioned soy that during the operation of drawing the l'adjacent sections of the boiler together by means of the da'w rods, the asbestos rope 55 in the outer curved sealing groove is compressedV so as to form a relatively denser flue gas imperviousbead towards the inside of the boiler. For this purpose, ac'- cording to the present invention, the meeting lands 50, 52 are so formed that when the boiler sections aredrawn fully together, to the position shown in Fig. 8, the gap i60' separating the inside edges 61, 62 of the boiler section outer Wall 54 is smaller than the gap 63 separating the The draw rods 59 when drawing the adjacent boiler sections together act vto' compress the asbestos rope 55- and actually extrude it into the gaps 60, 63 separating the sections to each side of the sealing rope. By providing a larger space towards the outside edge of the outer wall of the sections, however, the compressed asbestos rope is allowedy to escape somewhat, providing compression relief, while the portion of asbestos rope towards the inside of the boiler While the configuration chosen to illustrate this aspect of the invention is specific in its detail, modifications will be obvious to a man skilled in the art.

After the remaining sections are drawn into place by means of the draw rods 59, the lower nipple ports 46 around the top ofthe base 45 must be sealed with asbestos cement.

In the erection of the sections, when the sealing asbestos "rope 55 is laid in the sealing groove 50, 52 along the outer wall 54 of the boiler, the rope 55 is laid to extend across cleanout openings 70 which are formedin theouter wall of the boiler on the top of the sections. These cleanout openings 70 are formed by opposed rectangular-shaped cutout portions 71, 72 cast in the sectionswhich together, as shown in Fig. 2, form a cleanout opening between adacent boiler sections. According to the present invention, these cleanout openings are provided with a remov- Referring to Figs. 2, 9 and l0, the boiler sections are cast with locking lugs 74, 75 along the opposite sides of the cutout portions 71, 72 forming the cleanout openings 70. rIhese lockingY lugs slope from side to side of the boiler, and the opposite lugs together form part of a screw thread for receipt of a locking element 76 fastened to the plate employed for closing the cleanout openings. As shown in Figs. 9 and l0, the cleanout plate 73 has a raised bead 77 which extends into the cleanout opening to form abetter seal, and centrally of the plate carries the depending locking element, consisting, as shown, of cppo'sitely facing arms 78, 79 slightly twisted to engage the undersurfaces of the opposite lock- `ing lugs 74, 75. The lock element 76vis mounted on a pin or shaft 80 which is accessible by means Nof a hex cap 81 or the like on the top of the plate. To lockthe plate in place, the plate is' lowered' with the arms ofthe' element 76 used for locking the plate in place pivoted so as-to Ypass Without contact the lockingV lugs on the oppositeedges of the cleanout opening. The'elefnent is-then turned; when the plate is iny place, Ybymeans of the heX'cap'and a wrench, until the arms engage the vundersurfacef the locking lugs to" hold the plate in place.

These cleanout openings providev access to both the vertical uptakes 21' and the centrally located collector and the horizontal flue galleries 15 thereof withinthe boiler. This may be observed from an examination of=.Figs.w3-5 which reveal that the cleanout opening 70 is located in the present instance, at the upperl termini of the uptakes 21 and slightly towards the center lineV of the boiler on the axis of these uptakes, so that the cleaning implementma'y be inserted through the cleanoutgopenings and will reach into the uptakes to cleanl the Walls or flue gasV passage surface which may become covered with sooty deposits. The same is true of the horizontal flue galleries of the collector located centrally `of the boiler, for access is provided vof said sections being formed to leave a larger gap between said sections outwardly ofl said channels than inwardly of said channels, said rope'when so compressed forming a denser portion towards the inside Wall of the boiler, the larger gap affording relief allowing said' rope to squeeze towards the outside vwall of the boiler.

2. In a sectional boiler having a plurality of spacedfsections, means providing opposed: channels inthe facing edges of the adjacent boiler sections, heatresistant exible asbestos rope confined in said channels, theedges of said sections being formed to leave a larger gap between said sections outwardly of said channels than inwardly of said channels, and means for tying said sections` together, said latter means being effective for compressing said' rope'in said channels, said rope when so compressed forming; a relatively denser gas impervious bead running along the inside wall Yof the boiler, the larger gap` affording relief allowing said rope to squeeze outwardly between` the edges of the boiler sections toward the outside wall of the boiler, for sealing between sections `of the boiler.

3. In a boiler adapted to be .erectedona fire 'box' and formed to define, when so erected, a combustionicha'mber over the fire box, the combination comprising, fully enclosed water-backed uptakes extending from said combustion chamber vertically for receiving substantiallyie'qual shares of the gas produced in the combustiony chamber, said uptakes being regular in cross-section'and" extending nninterruptedly from the combustionchambertol the top of the boiler, and a horizontal collector extending the length of the boiler located centrally thereof and below the upper termini of said uptakes'fo'r receiving the streams of flue gas from the uptakesifmeans providing a turnaround passage at the upperv part' of each of theuptakes through which the flue gaso'ws'to said collector, each uptake being tapered from alarger crtsslsectional area at the mouth thereof where theuptake'p'ens'into the com bustion chamber, so that the velocity of the flue gas remains uniform the length of the uptake, said tum-around passage introducing substantiallygreater resistance tonne 1N)Y gas flow than is offered by the enclosed, regular, vertical uptake passage leadingtfrom the combustion chamber.`

4. In a sectional boiler having a front end sectinga back end section, a predetermined numberof like termedia'teV sections, vthe sections being adapted to be erected on a :lire box, said sections being formed-to define,

when so erected, a combustion chamber over the re box, the combination comprising, f ully enclosed water-backed uptakes extending from said combustion chamber vertically between each of the boiler sections at the sides of the boiler for receiving substantially equal shares of the gas produced inthe combustion chamber, said uptakes being regular in cross-section and extending uninterruptedly from the combustion chamber at the top of the sections, and a horizontal collector extending the length of the boiler located centrally thereof and below the upper termini of said uptakes for receiving the streams of llue gas from the uptakes, means providing a turn-around passage at the upper part of each of the uptakes through which the Hue gas flows to said collector, each uptake being tapered from a larger cross-sectional area at the mouth thereof where the uptake opens into the combustion chamber, so that the velocity of ilue gas remains uniform the length of the uptake, said turn-around passage introducing substantially greater resistance to flue gas ow than is olered by the enclosed, regular, vertical uptake passage leading from the combustion chamber.

5. In a sectional boiler having a plurality of separate sections erected on a lire box and defining a combustion chamber over the fire box, the combination comprising, means providing passages in the boiler sections and primary and secondary heating surfaces for heat transfer to water in said passages from the ue gas produced in the combustion chamber, uptakes defined between each of the boiler sections at the sides of the boiler for receiving the flue gas produced in the combustion chamber, a portion of said primary heating surface being provided by the lower regions of said uptakes, a portion of said secondary heating surface being provided by the upper regions of said uptakes, and a collector located centrally of the boiler and below the upper termini of said uptakes and extending the length of the boiler, for receiving the flue gasfrom the uptakes, means providing a turn-around passage at the top of each of the uptakes through which the ue gas ows to said collector, said uptakes being regular in cross-section and providing a continuous, uninterrupted path through which the ue gas ows to the collector, said turn-around passages introducing substantially greater resistance to ow of ue gas than is offered by the regular, vertical uptakes, the ilue gas from the combustion chamber being substantially divided between the uptakes of the boiler by the greater resistance to ow of said turn-around passages, said collector comprising a plurality of horizontal galleries providing the remaining portion of said secondary heating surface, the lower and outer of said galleries having a larger crosssectional area than the upper and inner of said galleries for drawing the ue gas uniformly over said secondary heating surface.

6. In a boiler adapted to be erected on a lire box, and formed to define, when so erected, a combustion chamber over the iire box, the combination comprising, waterbacked uptakes extending from said combustion chamber uninterruptedly vertically to the top of the boiler, said uptakes being regular in cross-section and providing primary and secondary heating surfaces, and vertically separated water-backed horizontal galleries extending centrally of the boiler and below the upper termini of said uptakes, for receiving flue gas therefrom, means providing a turn-around passage at the upper part of each of the uptakes through which the ue gas flows to said collector, each said vertical uptake being tapered from a larger area at the mouth thereof where the uptake opens into the combustion chamber so as to provide a relatively greater primary heating surface and so that the velocity of the lue gas remains substantially uniform the length of said uptake, said turn-around passage introducing substantially greater resistance to the flue gas flow than is offered by the vertical uptake so that each uptake receives a substantially equal share of the ue gas produced in the combustion chamber, thereby to obtain uniform distribution of ue gas over the secondary heating surface provided by the uptakes, said galleries providing additional secondary heating surface, the lower of said galleries having a larger cross-sectional area than the upper thereof for drawing a portion of the ue gas downwardly into the lower gallery, so that a uniform distribution of ue gas is obtained.

References Cited in the le of this patent UNITED STATES PATENTS 572,005 Grote Nov. 24, 1896 639,574 Hoiman Dec..19, 1899 676,340 Porter June l1, 1901 877,937 Mackay Feb. 4, 1908 1,551,642 Cripps Sept. 1, 1925 2,314,581 Gerich Mar. 23, 1943 2,535,507 Muller Dec. 26, 1950 FOREIGN PATENTS 345,391 Germany Apr. 25, 1920 185,205 Great Britain Aug. 28, 1922 

